1. Field of the Invention
This invention pertains generally to rectifier circuits and more particularly three-phase rectifier bridges or SCR Bridges for converting alternating current (AC) to direct current (DC).
2. Background Information
AC three-phase rectifiers are commonly employed to convert AC signals to DC. These circuits commonly use semiconductor controlled rectifiers disposed in bridge segments; typically one for each polarity of each phase. The firing point for each rectifier in the cycle of the AC waveform is normally controlled by a bridge firing circuit. It is not uncommon for a number of bridges to be operated in parallel with each bridge firing circuit being controlled by a central firing circuit. The central control circuit manages each of the bridge firing circuits so that the corresponding rectifiers in each of the parallel bridges conducts current at the exact same point in the AC signal waveform.
It's desirable to have each of the semiconductor controlled rectifiers in each corresponding segment of the several bridges fired at the exact same time to ensure the quality of the DC signal output and avoid the necessity for extensive filtering circuits. Unfortunately, even slight variations in the nature of the components can vary the resistance and inductance of the segments, affecting their outputs and resulting in some imbalance. The imbalance can further affect the heating of the various components in the different segments, further affecting the outputs.
Accordingly, an improved rectifier control scheme is desired that can maintain the balance between rectifiers of corresponding segments of parallel bridges as well as control the overheating of the individual rectifiers.